The description of the field sites experimental design and site and soil characteristics are already described in this issue by Houlbrooke et a/. (2004) (Chapter 4).
5.3. 1 Experimental procedure
In conjunction with the deferred irrigation research (Houlbrooke et a/. 2004 ( Chapter 4)), the performance of two types of small FOE travelling irrigators has been assessed . Travelling irrigators are propelled forward by the ejection of FOE from the rotating arms. In the first two seasons of the study (2000101 & 200 1 /02), a 'Briggs Model 1 5' standard rotating travelling irrigator (hereafter referred to as a 'rotating irrigator') was evaluated. I n the third season of this study (2002/03), a 'Spitfire' (mark I) oscillating boom travelling irrigator (hereafter referred to as an 'oscillating irrigator') was evaluated. Ouring the second of these first two seasons the rotating irrigator was modified in an attempt to improve its application uniformity.
During FOE applications, each irrigator was set up to move along a continuous path of travel down the length of the plots, which were arranged in a single row. Adjustable speed settings on each of the irrigators allowed the FOE application depth to be set to a depth within the range of 6 - 36 mm for the rotating irrigator and 1 0 - 48 mm for the oscillating irrigator. FOE was pumped to the travelling irrigator from the aerobic pond of a standard two pond treatment system.
The depth and the uniformity of application under the irrigators were measured using a series of catch containers (each 430 mm long x 300 mm wide), which were arranged at 2-m spacing in a single row across the pathway of the irrigator. The containers were arranged so as to cover the entire distance from the irrigator to the outer edge of the 'throw', on both sides of the irrigator. Irrigator travel speed was assessed by timing how long it took the irrigator to travel 40 m. The average application rates (mm min-1) of the different irrigators used were calculated using average travel speeds and the longitudinal diameter of the irrigation swath. For example an application depth of 1 5 mm would be divided by the time required for the irrigator to pass over an irrigation swath width .
A standard rotating irrigator (Heatley, 1 996) was used to apply F DE to the experimental area in the 2000101 season. The irrigator requires an irrigation pressure between 1 50- 250 kPa. A rubber sleeve was fitted to the end of the booms to create a 1 0 mm nozzle.
In the 2001 /02 season , modifications were made to the rotating irrigator in an attempt to improve its application uniformity. These modifications included using irrigator splash plates or a custom-built irrigation bar, which was designed to divert more FOE to the centre of the application profile. The splash plates were approximately 450 mm long and 80 mm wide with a 45 degree change in angle at the end. They were attached to each end of the rotating booms of the irrigator to help disperse FDE as it came out of the nozzles, thereby widening the application swath width (the width that is instantaneously wet from one pass of the irrigation nozzle) (Plate 5. 1 ) . The use of splash plates on the rotating irrigator to disperse or enlarge the irrigation swath, and to improve the application uniformity, was investigated during the 2001 /02 irrigation season. A number of different splash plate configurations were studied.
The irrigation bar used in the modifications was attached to the centre frame of the rotating irrigator at a height of 1 m above the ground (Figure 5. 1 ) . The bar was 4 m long and had three low-pressure emitters (2 m spacing) , one emitter in the middle of
Chapter 5: The perfonnance of travelli ng effluent irrigators
the bar and the other two at each end. Each emitter had an outside spray radius of 2 m, wh ich provided the irrigator bar with a total spray coverage width of 8 m. Approximately 0.5 litre sec-
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which equated to 1 0% of the irrigator's total flow, could be diverted through the irrigator bar without seriously compromising the travel speed of the irrigator.Plate 5 . 1 Splash plate strapped on to the end of a rotating boom arm of a standard rotating irrigator.
Main irrigation swath
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� �Irrigator nozzles -. , ,
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Diverting pipe
Figure 5.1 Standard travelling irrigator with an additional irrigation bar strapped to the middle of the irrigator. Water is diverted to the bar from the main pipe line.
The appl ication pattern of a new technology, oscillating travelling irrigator was evaluated, in the 2002/03 season. The oscillating irrigator that was used has a long-
range, flick-over nozzle on a single oscillating 1 8 mm boom that allows for 1 800 coverage (Plate 5.2). The irrigator is self propel led, has electronic control of application depth and operates between pressures of 1 50 to 280 kPa. Because the oscillating irrigator's boom flicks from side to side, without doing a full circumference, it is likely to have a different application pattem to that observed for the rotating i rrigator. A governor added to the irrigator was designed to eliminate longitudinal variation in application depth .
Plate 5.2 Mark 1 'Spitfire' oscillating irrigator in operation with single boom and flick nozzle to achieve 1800 coverage.
The authors acknowledge that the method used to evaluate the application uniformity of the irrigators did not conform to standardised engineering testing protocols (BS EN ISO 1 1 545:200 1). This is because the aim was to operate the irrigators as close to farmer practice as possible in order to assess the influence of appl ication uniformity on direct drainage of partially-treated FOE.